The contents of all the publications cited in this application, or comparable sources which are quoted, in order to explain the background of the invention are incorporated in the present application for the purpose of the disclosure.
G-protein coupled receptors represent a superfamily of cell membrane-associated receptors which play an important part in numerous biochemical and pathobiochemical processes in mammals and especially in humans. All GPCRs consist of seven hydrophobic, transmembrane alpha-helical domains which are connected together by three intracellular and three extracellular loops and have an extracellular amino terminus and an intracellular carboxy terminus. One or more heterotrimeric G proteins are involved in their cellular signal transduction. Diverse physiological stimuli such as photosensitivity, taste and odor, but also fundamental processes such as metabolism, reproduction and development are mediated and controlled by them. GPCRs exist for exogenous and endogenous ligands. Peptide hormones, biogenic amines, amino acids, nucleotides, lipids, Ca2+, but also photons, have inter alia been identified as ligands; moreover one ligand may activate different receptors.
According to a recent investigation, 367 sequences have been identified in the human genome for G-protein coupled receptors (GPCRs) with endogenous ligands, D. K. Vassilatis et al., PNAS 100(8), 4903-4908 (2003). Of these, 284 belong to class A, 50 to class B, 17 to class C and 11 to class F/S. Examples belonging to class A are the bombesin, the dopamine and the LHRH receptors, and to class B are the VIP and the calcitonin receptors. The natural ligands for numerous GPCRs are as yet unknown.
Owing to their function, GPCRs are suitable as targets for medicaments for the therapy and prevention of a large number of pathological conditions. It is speculated that about 50% of currently known targets for active ingredients are GPCRs [Y. Fang et al., DDT 8(16), 755-761 (2003)]. Thus, GPCRs play an important part in pathological processes such as, for example, pain (opioid receptor), asthma (β2-adrenoceptor), migraine (serotonin 5-HT1B/1D receptor), cancer (LHRH receptor), cardiovascular disorders (angiotensin receptor), metabolic disorders (GHS receptor) or depression (serotonin 5-HT1a receptor), K. L. Pierce et al., Nat. Rev. Mol. Cell Biol. 3, 639-650 (2002).
General information about GPCRs is to be found under http://www.gpcr.org.
The present invention describes novel ligands with improved properties for GPCRs in general, the compounds provided by the invention acting in particular as antagonists of the LHRH receptor.
The natural ligand of this receptor, the peptide hormone LHRH, is synthesized in cells of the hypothalamus and released in pulsatile fashion from the hypothalamic neurons into the capillary plexus of the ementia mediana. In the anterior lobe of the pituitary, LHRH binds to the LHRH receptors of the gonadotropic cells and stimulates certain trimeric G-proteins, which initiate a branched signal transduction cascade. The initial event is activation of phospholipase C, A2 and/or D. This leads to an increased provision of the second messengers diacylglycerol and IP3, followed by Ca2+ mobilization from intracellular pools, and activation of various subordinate protein kinases. Finally, there is stimulation of the production and temporally defined pulsatile release of the gonadotropins FSH and LH. The two hormones are transported via the circulation to the target organs the testes and ovaries respectively. There they stimulate the production and release of the appropriate sex hormones. In the opposite direction there is a complex feedback mechanism by which the concentration of the sex hormones formed in turn regulates the release of LH and FSH.
In the male organism, LH binds to membrane receptors of the Leydig cells and stimulates testosterone biosynthesis. FSH acts via specific receptors on the Sertoli cells and assists the production of spermatozoa. In the female organism, LH binds to the LH receptors of the theca cells and activates the formation of androgen-synthesizing enzymes. FSH stimulates proliferation of granulosa cells of certain follicle stages via the FSH receptors thereof. The androgens which are formed are converted in the adjacent granulosa cells to the estrogens estrone and estradiol.
A number of disorders distinguished by benign or malignant tissue proliferations depend on stimulation by sex hormones such as testosterone or estradiol. Typical disorders of this type are prostate cancer and benign prostate hyperplasia (BPH) in men, and endometriosis, uterine fibroids or uterine myomas, pubertas praecox, hirsutism and polycystic ovary syndrome, and breast cancer, uterine cancer, endometrial cancer, cervical cancer and ovarian cancer in women.
Since its discovery in 1971 by Schally et al. Science 173, 1036-1038 (1971), more than 3000 synthetic analogues of natural LHRH have been synthesized and tested. Peptide agonists such as triptorelin and leuprolide have been established for many years successfully in the therapy of gynecological disorders and cancers. However, the disadvantage of agonists is generally that they stimulate LHRH receptors in the initial phase of use and thus lead to side effects via an initial increase in the sex hormone levels. Only after downregulation of the LHRH receptor as a result of this overstimulation can the superagonists display their effect. This leads to a complete reduction in the sex hormone levels and thus to pharmacological castration with all the signs and symptoms. This disadvantage is associated with the impossibility of targeted adjustment of the level of sex hormones via the dosage. Thus, therapy of diseases which do not require a total reduction of the sex hormone levels to the castration level, such as, for example, benign tissue proliferations, with an agonist is not optimal for the patient.
This has led to the development of peptide LHRH receptor antagonists, of which, for example, cetrorelix (Cetrotide®) has been successfully introduced for controlled ovarian stimulation in the context of the treatment of female infertility. The antagonists inhibit the LHRH receptor immediately and dose-dependently, and thus lead to an immediate reduction in the plasma levels of testosterone or estradiol and progesterone. The peptide antagonists are, however, somewhat less potent than the agonists, and thus higher doses must be given.
A review of the clinical applications and the potential of LHRH agonists and antagonists is given by R. P. Millar et al. in British Med. Bull. 56, 761-772 (2000) and R. E. Felberbaum et al., Mol. Cell. Endocrinology 166, 9-14 (2000) and F. Haviv et al. in Integration of Pharmaceutical Discovery and Development: Case Studies, Chapter 7, ed. Borchardt et al., Plenum Press, New York (1998). Besides the treatment of malignant and benign neoplastic diseases, further possible applications are controlled ovarian stimulation in the context of in vitro fertilization, fertility control (contraception), and protection from unwanted side effects of radio- or chemotherapy, the treatment of HIV infections (AIDS) and of neurological or neurodegenerative disorders such as Alzheimer's disease. Specific LHRH receptors have not only been found on pituitary cells, but also on cells in various tumors, e.g. of the breast and ovaries. These receptors might mediate a direct antiproliferative effect of LHRH receptor antagonists on the tumor.
The peptide LHRH receptor agonists and antagonists are mostly decapeptides whose bioavailability is inadequate for oral administration. They are typically given as solutions for injection or as depot formulation, subcutaneously or intramuscularly. This application is associated with inconveniences for the patient, and the compliance suffers. In addition, synthesis of the decapeptides is complicated and costly.
It is therefore sensible to look for non-peptide LHRH receptor antagonists which, besides high activity, have an improved metabolic stability and can be administered orally.